Along with various portable electric devices, including e.g., mobile phones, personal digital assistants (PDA) and notebook computers, compact, light weight, and low power-consuming flat panel display (FPD) devices continue to be developed, including liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and vacuum florescent displays (VFDs). Owing to the ease with which they are driven, and to their superior ability to display images, LCDs are becoming widely used.
An LCD device displays information on a screen by refractive anisotropy. As illustrated in FIG. 1, an LCD device 1 typically comprises a lower substrate 5, upper substrate 3 and a liquid crystal layer 7 therebetween. The lower substrate 5, also referred to as the driving device array substrate, includes a plurality of pixels (not shown), in which each pixel includes a driving device (e.g., a thin film transistor (TFT)) and a pixel electrode. The upper substrate 3, also referred to as the color filter substrate, includes common electrode and a color filter layer for producing color. An alignment layer is formed on each of the lower and upper substrates 5 and 3 for aligning liquid crystal molecules in the liquid crystal layer 7.
The lower substrate 5 and the upper substrate 3 are attached to each other by a sealant material 9, formed at peripheral regions thereof. The liquid crystal layer 7 is confined within an area defined by the peripheral regions. Light transmittance of the pixels is controlled by electric fields generated between pixel pixel electrodes in the driving devices and the common electrode. The generated electric fields reorient liquid crystal molecules in the liquid crystal layer 7 to display a picture.
FIG. 2 is a flow chart illustrating a related art method for fabricating the LCD device. The flow chart depicts three sub-processes: a TFT array substrate forming process; a color filter substrate forming process; and a cell forming process. Step S101 depicts a TFT array substrate forming process whereby a plurality of gate lines and data lines are formed on the lower substrate 5 (e.g., a glass substrate), thereby defining an array of pixel areas. TFTs are connected to the gate lines and the data lines within each pixel area; pixel electrodes connected to the TFTs drive a liquid crystal layer according to a signal applied through the TFT.
In step S104, a color filter process is used for producing predetermined colors whereby R, G and B color filter layers and a common electrode are formed on the upper substrate 3 (i.e., a glass substrate). In steps S102 and S105, alignment layers are formed over the entire surface of the lower substrate 5 and the upper substrate 3. Alignment layers are rubbed to induce predetermined surface anchoring characteristics (i.e., a pretilt angle and alignment direction) within the liquid crystal molecules of the liquid crystal layer 7.
In step S103, spacers are dispersed onto the lower substrate 5. In step S106, the sealant material is printed at peripheral regions of the upper substrate 3. In step S107, the lower and upper substrates 5 and 3 are pressed and bonded together (i.e., assembled). Dispersal of the spacers in step S103 ensures that a uniform cell gap is formed between the assembled lower and upper substrates 5 and 3, which are large glass substrates.
In step S108, the assembled upper and lower substrates 5 and 3 are cut into unit panels. Specifically, each of the upper and lower substrates 5 and 3 includes a plurality of unit panel areas, within which individual TFT arrays and color filters are formed. In step S109, liquid crystal material is injected into the cell gap of each unit panel through a liquid crystal injection hole in the sealant material. After each cell gap is completely filled with liquid crystal material, the liquid crystal injection hole is sealed.
In step S110, the filled and sealed unit panels are tested. The LCD panel is tested by an appearance test and a lighting test. The lighting test determines whether each electric device is operating normally by applying a signal to a completed LCD panel. The appearance test evaluates imperfections in the LCD panel that are detectable to the naked eye.
A LCD panel test apparatus includes a testing table containing a lamp for outputting light. Upon completing the steps for fabricating an LCD panel, the LCD panel is transferred to the testing table of the LCD panel test apparatus and a polarizing plate is positioned on the LCD panel. Then, a signal is applied to the LCD panel, such that the light from the lamp on the testing table becomes incident on the LCD panel. An operator can determine if the LCD panel is defective by observing the passage of light through the LCD panel.
When testing the LCD panel, light passes through both the LCD panel and the polarizing plate. It is important to align the LCD panel with the polarizing plate. If the LCD panel is not aligned with the polarizing plate, the operator may mistakenly judge the LCD panel as being defective. Accordingly, the LCD panel test apparatus includes a camera to align the LCD panel with the polarizing plate. is the camera is used to photograph an alignment mark on an outer surface of the LCD panel. The photographed alignment mark allows an evaluation of alignment state between the LCD panel and the polarizing plate.
The camera is positioned just above the alignment mark of the LCD panel. Accordingly, when the polarizing plate is attached or detached from the testing table, the polarizing plate may inadvertently contact the camera. As a result, the LCD panel may be subsequently misjudged as being defective.